From 0bdc53e82965710e76071b3948a62f46dffea531 Mon Sep 17 00:00:00 2001 From: ackman678 Date: Fri, 21 Oct 2016 12:50:32 -0700 Subject: [PATCH] mol signaling neurons lecture init --- .gitignore | 1 + 2016-10-16-lecture08.md | 998 ++++++++++++++++++---------------------- 2016-10-16-lecture09.md | 621 +++++++++++++++++++++++++ 3 files changed, 1067 insertions(+), 553 deletions(-) create mode 100644 2016-10-16-lecture09.md diff --git a/.gitignore b/.gitignore index 2182f31..1e61af1 100644 --- a/.gitignore +++ b/.gitignore @@ -1,2 +1,3 @@ .DS_Store figs +tmp diff --git a/2016-10-16-lecture08.md b/2016-10-16-lecture08.md index 93fab82..139fa54 100644 --- a/2016-10-16-lecture08.md +++ b/2016-10-16-lecture08.md @@ -1,166 +1,180 @@ ## Neurotransmitter receptors -* Embedded in the plasma membrane of post-synaptic cell. -* Either are ion channels themselves (ionotropic, or ligand-gated ion channel) or interface with ion channels (metabotropic, or G-protein coupled receptors). -* Ultimately, the binding of neurotransmitter causes opening of channels and ion flux. This can lead to depolarization or hyperpolarization of the membrane potential depending on the ion concentrations and the particular ion species flowing in or out. +* Embedded in the plasma membrane of post-synaptic cell +* Two classes of neurotransmitter receptors– + * receptors that are ion channels themselves (**ionotropic** or 'ligand-gated' ion channel) + * receptors that interface with separate ion channels (**metabotropic**, or G-protein coupled receptors) +* Ultimately, the binding of neurotransmitter results in the opening of ion channels and ion flux. This leads to either depolarization or hyperpolarization of the membrane potential depending on the **types of ions** flowing through the channel pores and the ions' respective **electrochemical driving forces** Note: -Today we will dive a bit deeper into the structure and function of neurotransmitter receptors. +Today we will dive a bit deeper into the structure and function of neurotransmitter receptors... last time was a warm up + +For synaptic transmission, neurotrans receps are generally located in the post-synaptic membrane (*though there are exceptions, e.g. some transmitter receptors may be located on pre-synaptic membrane or at non synaptic site in the cell*). + +Two classes... + +In either case, neurotransmitter binding will result in ion channels opening and ion flux across the post-synaptic membrane. Whether this results in hyperpolarization or depolarization of the membrane will be due to the types of ions flowwing through the channels and their respective electrical/chemical driving forces (Nernst) + + +-- + +## Midterm 1 + +```r +mean 84.4 +median 85.5 +std 7.8 +max 98 +min 58.5 +``` --- ## Ionotropic neurotransmitter receptors -Neurotransmitter binds receptor +* Neurotransmitter binds receptor +* Channel opens, allowing ions to flow through -Channel open allowing ions to flow through +
Neuroscience 5e Fig. 5.3
+
Neuroscience 5e Fig. 5.16
-
Note: - The ionotropic receptors are the ones you’ve probably seen in our synaptic diagrams so far, where NT binds directly to an ion channel pore, causing it to open and allow ions to move through the pore. ---- - -## Ionotropic neurotransmitter receptors - -
- -Note: - -neurotransmitter binds - -channel opens - -ions flow across membrane +* neurotransmitter binds +* channel opens +* ions flow across membrane --- ## Metabotropic neurotransmitter receptors -
+
Neuroscience 5e fig. 5.16
+ Note: -neurotransmitter binds +Metabotropic transmitter receptors are G-protein coupled receptors, also known as seven-transmembrane domain receptors in you cell biology courses. -g protein is activated - -g protein subunits or intracellular messengers modulate ion channels - -ion channel opens - -ions flow across membrane +* neurotransmitter binds +* g protein is activated +* g protein subunits or intracellular messengers modulate ion channels +* ion channel opens +* ions flow across membrane --- -## Title Text +## Neurotransmitter receptors video summary -[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation05-03IonotropicandMetabotropicReceptors.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation05-03IonotropicandMetabotropicReceptors.mov) - -
+
Neuroscience 5e Animation 5.3
Note: - --- -## Nicotinic acetylcholine (nACh) receptors +## Nicotinic acetylcholine receptors (nAChR) -* Ion-channel receptor (ionotropic) -* ACh binds nACh receptor– opens up -* ACh causes nACh receptor to open transiently and stochastically (patch clamp studies). -* An action potential causes lots of ACh molecules to be released simultaneously, transiently opening many nACh receptors. -* The summed current flow into the muscle cell is called the end plate current (EPC). Current flow changes the potential of the muscle, the EPP, which can trigger an action potential. +* Ionotropic receptor +* ACh binds the nAChR– opens the channel +* ACh causes nAChR to open transiently and stochastically (patch clamp studies) +* An action potential causes lots of ACh molecules to be released simultaneously, transiently opening many nACh receptors +* The summed current flow into the muscle cell is called the end plate current (EPC). Current flow changes the transmembrane potential of the muscle, the end plate potential (EPP), which triggers an action potential Note: -nACh Receptors are ionotropic receptors and are the receptor you’ve heard the most thus far, being the one that underlies end plate currents at the neuromuscular junction that cause end plate potentials. +So to understand the properties of ionotropic neurotransmitter receptors lets start with the nicotinic ACh receptor (abbreviated nAChR). ---- +nACh Receptors are ionotropic or ligand-gated receptors where the ligand is ACh and are the receptor you’ve heard the most thus far, being the one that underlies end plate currents at the neuromuscular junction that cause end plate potentials in muscle cells. -## Outside-out patch clamping showing ACh gated currents - -Neuroscience 5e 5.17 - -Channels open for various amounts of time at a given potential. - -
- -Note: - -The binding of a neuro-transmitter to its receptor usually opens (sometimes closes) ion channels. - -The figure shows a simple case. In the absence of ACh, the channel is closed. In the presence of high ACh (the channel always has ACh bound), the channel opens and closes. These repeated breif openings are seen as downward deflections corresponding to inward current. +ACh causes... --- -## Activation of nACh receptors at neuromuscular synapses +## Patch clamping shows ACh gated currents through nicotinic ACh receptors -post-synaptic muscle cell voltage clamped to look at currents +
Patch clamp recording of current through single nAChR. Channels open for varying amounts of time while ACh is bound.
Neuroscience 5e Fig. 5.17
-not voltage clamped, inward EPC causes depolarizing EPP in the muscle cell - -Neuroscience 5e 5.17 - -
- -
Note: -The traces show inward currents through these ionotropic ACh channels, showing the currents stemming from a single channel, 10 channels, and a million channels. +The binding of a neurotransmitter to its receptor usually opens (*sometimes closes*) ion channels. -As we will learn in a few minutes, the channel opened by ACh lets mostly Na+ through resulting in these inward currents that depolarize the muscle cell, resulting in EPPs and typically resulting in APs as we’ve discussed before. +The figure shows a simple case. In the absence of ACh, the nAChR is closed. In the presence of high [ACh] (the channel always has ACh bound), the channel opens and closes. These repeated brief openings are seen as downward deflections corresponding to inward current. Notice the current amplitudes in this patch clamp trace below are unitary or quantal indicating that a single channel is being recorded in this case... + +These look like microscopic currents you get in single channel patch clamp recordings like we discussed previously. + +If this piece of membrane and channel is from a muscle cell than a bunch of these currents put together are the ones that give rise to the end plate potentials we for muscle cells before. + + +--- + +## Activation of nAChR at neuromuscular synapses + +
end plate currents in a voltage-clamped muscle cell
Neuroscience 5e Fig. 5.17
+ +
+
+depolarizing end plate potential recorded in muscle cell due +to the inward end plate currents +
Neuroscience 5e Fig. 5.17
+ +Note: + +Indeed imagine we are doing an experiment where we stimulate a motor neuron and we record end plate currents in a muscle cell... + +...then these traces on the left show inward currents through these ionotropic ACh channels in the muscle cell, showing the currents stemming from a single channel, 10 channels, and hundreds of thousands of channels. Notice the amplitudes of the currents scale. + +...and this panel on the right shows postsynaptic potential change or end plate potential produced by the EPC as we discussed previously + +As we will learn in a few minutes, the channel opened by ACh lets mostly Na⁺ through resulting in these inward currents that depolarize the muscle cell, resulting in EPPs and typically resulting in APs as we’ve discussed before. [from http://www.ncbi.nlm.nih.gov/books/NBK21586/: ](http://www.ncbi.nlm.nih.gov/books/NBK21586/) -* acetylcholine causes opening of a cation channel in the receptor capable of transmitting 15,000 – 30,000 Na+ or K+ ions a millisecond +* *acetylcholine causes opening of a cation channel in the receptor capable of transmitting 15,000 – 30,000 Na⁺ or K⁺ ions a millisecond* * - >Two factors greatly assisted in the characterization of the nicotinic acetylcholine receptor. First, this receptor can be rather easily purified from the electric organs of electric eels and electric rays; these organs are derived from stacks of muscle cells (minus the contractile proteins) and thus are richly endowed with this receptor. (In contrast, this receptor constitutes a minute fraction of the total membrane protein in most nerve and muscle tissues.) Second, α-bungarotoxin, a neurotoxin present in snake venom, binds specifically and irreversibly to nicotinic acetylcholine receptors. --- -## How do we figure out what ions flow through the nACh receptor? +## How do we figure out what ions flow through the nicotinic ACh receptor? -* From Nernst equation– the equilibrium potential of a cell is the potential at which there is a balance between the concentration gradient and the electrochemical gradient. -* In other words– there is no net flow of ion x at the equilibrium potential, Ex. -* Thus if one measured the ACh dependent current flow at different potentials, one could determine the potential that current flow was 0. This is called the reversal potential or Erev. -* The end plate current (EPC) is therefore IACh and is equal to the driving force on an ion multiplied by its permeability (remember Ohms law: I = gV). -* IACh = gACh(Vm-Erev) -* Predicts that current will be inward at potentials more negative than Erev, becomes small at potentials approaching Erev, and then becomes outward at potentials more positive then Erev. +
+
+ +* Recall from Nernst equation– the equilibrium potential of a cell for ion *x* is the potential at which the electrochemical driving forces is balanced for ion *x* (i.e there is no net flow of ion *x* at the equilibrium potential *Ex*) +* Thus if one measured the ACh dependent current flow at different potentials, one could determine the membrane potential (*Vm*) where current is 0. This is called the **reversal potential** or *Erev* +* The end plate current (EPC) at the muscle cell must therefore be *IACh* and is equal to the driving force on an ion multiplied by its permeability (remember Ohm's law: *I = gV*) +* *IACh = gACh(Vm – Erev)* +* Predicts that current will be inward at potentials more negative than *Erev*, becomes small at potentials approaching *Erev*, and then becomes outward at potentials more positive then *Erev* + +
Note: -Use our good friend the Nernst eqn, which you can recall is… +Now using our good friend the Nernst eqn, which you can recall is… -Since we know there isn’t any net flow of an ion x, at the Ex, we can measure the ACh dependent currents at different potentials and figure out the potentials at which current flow is 0. +Since we know there isn’t any net flow of an ion x, at the Ex, we can measure the ACh dependent currents at different potentials and figure out the potentials at which current flow is 0. +When we are talking about the potential at which postsynaptic currents like the endplate current reverses from inward net ion flux to outward net ion flux, we call this potential the reversal potential denoted Erev. +We can call the endplate current then the IAch or the current flowing through the ACh receptor at skeletal muscle endplate membrane and IAch is therefore equal to the driving force (which is the difference between Vm and Erev) multiplied by the permeability for ACh gAch. -When we are talking about the potential at which postsynaptic currents like the endplate current reverses from inward net ion flux to outward net ion flux, we call this potential the reversal potential denoted Erev. +This would then predict that current will be inward at potentials more negative than Erev… - - -We can call the endplate current then the IAch or the current flowing through the ACh receptor at skeletal muscle endplate membrane and IAch is therefore equal to the driving force (which is the difference between Vm and Erev) multiplied by the permeability for ACh gAch. - - - -This would then predict that current will be inward at potentials more negative than Erev… - -* - Predicts that current will be negative (inward) at potentials more negative than Erev, becomes small at potentials approaching Erev, and becomes positive (outward) at potentials more positive then Erev. +* Predicts that current will be negative (inward) at potentials more negative than Erev, becomes small at potentials approaching Erev, and becomes positive (outward) at potentials more positive then Erev. --- -## Influence of the postsynaptic membrane potential on end plate currents +## Influence of the postsynaptic Vm on end plate currents + +
voltage-clamping a postsynaptic muscle fiber
Neuroscience 5e Fig. 5.18
-
Note: @@ -171,32 +185,83 @@ A postsynaptic muscle fiber is voltage clamped to control the muscle fiber’s m ## Hypothetical ion channel selectivities and the reversal potential -
+
Current-voltage relationships for different ion selectivities
Neuroscience 3e 2001
+ Note: So let’s imaging what the current-voltage relationships would look like for different channel selectivities. Remember the reversal potential is when there there is no net ion flux, so it 0 nA on all these graphs and if a channel is selective to only K, it would be equal to the Ek. -If the channel was selective only to Na, than the Erev would be equal to ENa. Same for chloride. +If the channel was selective only to Na, than the Erev would be equal to ENa. Same for chloride. -If the channel was a non-selective cation channel (passing both K and Na) than +If the channel was a non-selective cation channel (passing both K and Na) then the current-voltage relationship would look like... 11Na, 12Mg, 17Cl, 19K, 20Ca + +*Ca2+ ions flow through CaV channels at a rate of ~106 ions s−1, but Na+ conductance is 500fold less through CaV channels* +*extracellular [Na+] is nearly 70fold higher than Na+, thus Ca2+ selectivity is crucial* +*Ca2+ and Na+ have nearly identical diameters (~2 Å)* +*Ca2+ selectivity from high affinity binding, preventing Na+ permeability. Multi site pore, with knock on mechanism to push Ca2+ ions through* [#Tang:2014] + +[#Tang:2014]: Tang, L., Gamal El-Din, T. M., Payandeh, J., Martinez, G. Q., Heard, T. M., Scheuer, T., Zheng, N., and Catterall, W. A. (2014). Structural basis for Ca2+ selectivity of a voltage-gated calcium channel, Nature, 505(7481), 56-61. PMID 24270805 + + +--- + +## Influence of the postsynaptic Vm on end plate currents + +
Effect of Vm on postsynaptic muscle fiber end plate currents
Neuroscience 5e Fig. 5.18, Takeuchi J Physiol 1960
+ + +Note: + +These little transients are just stimulus artifacts, but look at the postsynaptic end plate currents in these at these different Vms. Look what happens when Vm is at 0mV, there is no current and then above 0 mV it flips from being inward to net outward current... + +We already know that ACh is essential for the end plate currents-- therefore we can say that this EPC is IAch. Therefore what is the Erev for IAch? + + +--- + +## Influence of the postsynaptic Vm on end plate currents + +
Expected Erev if nAChR permeable only to K⁺, Cl⁻, or Na⁺
Neuroscience 5e Fig. 5.18
+
Observed Erev is in between Ek and ENa
Neuroscience 5e Fig. 5.18, Takeuchi J Physiol 1960
+ +Note: + +[#Takeuchi:1960]: Takeuchi, A. and Takeuchi, N. (1960). On the permeability of end-plate membrane during the action of transmitter, J Physiol, 154(), 52-67. PMID 13774972 + +--- + +## Influence of the postsynaptic Vm on end plate currents + +
Neuroscience 5e, Fig. 5.19, Takeuchi J Physiol 1960
+ + +Note: + +So it seems that the ACh activated ion channels are equally permeable to Na and K and this was tested in 1960 by Akira and Noriko Takeuchi by changing the extracellular concentration of these ions. As predicted, lowering [Na] shifts Erev to the left and and raising the external [K] shifts Erev to the right. + --- ## What ions flow through the nACh receptor? -* Voltage clamping experiments show that there are large inward currents at -110 mV, smaller currents at -60 mV and no current at 0 mV. Outward currents at +70 mV. Therefore Erev = 0. -* Erev is not at any of the equilibrium potentials for a single ion, lies in between K+ (-100 mV) and Na+ (+70 mV). -* Altering the K+ concentration or the Na+ concentration will change the membrane potential. Therefore both Na+ and K+ are permeable through the nACh receptor. -* nACh receptor can conduct both Na+ and K+ ions. The direction of flow is dependent on the membrane potential. The normal resting state of muscle is -100 mV, well below 0 mV (Erev) therefore normally at rest Na+ rushes in with very little K+ rushing out. +
+
+ +* Voltage clamping experiments show that there are large inward currents at -110 mV, smaller currents at -60 mV and no current at 0 mV. Outward currents at +70 mV. Therefore Erev = 0 +* Erev is not at any of the equilibrium potentials for a single ion, lies in between K⁺ (-100 mV) and Na⁺ (+70 mV) +* Altering the K⁺ concentration or the Na⁺ concentration will change the membrane potential. Therefore both Na⁺ and K⁺ are permeable through the nACh receptor +* nACh receptor can conduct both Na⁺ and K⁺ ions. The direction of flow is dependent on the membrane potential. The normal resting state of muscle is -100 mV, well below 0 mV (Erev) therefore normally at rest Na⁺ rushes in with very little K⁺ rushing out + +
Note: As we will see in a minute voltage clamp experiments show that there is a… -Erev… +Erev… Furthermore, altering… @@ -204,93 +269,40 @@ Therefore we can conclude that the nAChR can conduct both Na and K ions. --- -## Influence of the postsynaptic membrane potential on end plate currents -
+## Na⁺ and K⁺ movements during EPCs and EPPs -Note: - ---- - -## The effect of ion channel selectivity on the reversal potential - -K+ only permeable channel - -Cl– only permeable channelNa⁺ only permeable channel - -
- -
- -Note: - ---- - -## Influence of the postsynaptic membrane potential on end plate currents - -
- -Note: - -So it seems that the ACh activated ion channels are equally permeable to Na and K and this was tested in 1960 by Akira and Noriko Takeuchi by changing the extracellular concentration of these ions. As predicted, lowering [Na] shifts Erev to the left and and raising the external [K] shifts Erev to the right. - ---- - -## Na+ and K+ movements during EPCs and EPPs - --90 typical resting potential of a muscle - -depolarization - -hyperpolarization - -nothing - -Neuroscience 5e 5.20 - -
+
Neuroscience 5e Fig. 5.20
Note: Even though these ionotropic channels opened by ACh are permeable to both Na and K, at the resting membrane potential the EPC is generated primarily by Na influx because of the reduced driving force on K since at Vrest the membrane potential is closer to Ek. +In fact the Na⁺ and K⁺ permeabilities of the nAChR channel are similar, therefore the **magnitudes of the Na⁺ and K⁺ currents depends on the driving forces present for each ion** + --- -## Na+ and K+ movements during EPCs and EPPs +## Na⁺ and K⁺ movements during EPCs and EPPs -EPC: in or out - -EPP:depolarzing or - -hyperpolarizing - -Neuroscience 5e 5.20 - -
+
EPC: inward or outward; EPP: depolarizing or hyperpolarizing
Neuroscience 5e Fig. 5.20
Note: -Here is the key: you get inward currents at potentials more negative the Erev and you get outward currents at potentials more positive than Erev. +Here is the key: you get inward currents at potentials more negative the Erev and you get outward currents at potentials more positive than Erev. -The resulting EPPs depolarize postsynaptic cell at potentials more negative than Erev and potentials more positive than Erev hyperpolarize the cell. +The resulting EPPs depolarize postsynaptic cell at potentials more negative than Erev and potentials more positive than Erev hyperpolarize the cell. + +*Since the Na⁺ and K⁺ permeabilities of this channel are similar, the magnitudes of the Na⁺ and K⁺ currents depends on the driving forces present for each ion* + + --- -## Na+ and K+ movements during EPCs and EPPs +## nAChR summary -* Since the Na+ and K+ permeabilities of this channel are similar, the magnitudes of the Na+ and K+ currents depends on the driving forces present for each ion - -
- -Note: - - ---- - -## Think about it - -* At normal resting potentials as the nACh receptor opens, many Na+ ions rush in and a few K+ rush out. This causes the cell to depolarize. As the potential goes toward Erev, as many K+ go out as Na+ goes in. Therefore the nACh receptor if open long enough would drive the potential to Erev. If Erev is above threshold, the probability of an action potential happening is increased and is called an excitatory postsynaptic potential (EPSP) -* If Erev is below threshold the probability of an action potential is decreased. Called an inhibitory postsynaptic potential (IPSP). +* When the nAChR opens at normal resting potentials many Na⁺ ions rush in and a few K⁺ rush out. This causes a depolarizing EPP in the muscle cell. As the Vm during the EPP approaches Erev, outward K⁺ flux is equal to inward Na⁺ flux. Therefore if the nACh receptor is open long enough, it will drive Vm to Erev. +* If Erev is above action potential threshold, the probability of an action potential occurring is increased +* If Erev is below action potential threshold, the probability of an action potential occurring decreased Note: @@ -300,37 +312,31 @@ Note: --- -## Postsynaptic potentials between neurons - -* Excitatory postsynaptic potentials (EPSP) increases the likelihood that an action potential will be initiated in the post synaptic cell. -* Inhibitory postsynaptic potentials (IPSP) decreases the likelihood that an action potential will be initiated in the post synaptic cell. - -
- -Note: - -In fact we can generalize the properties that we’ve learned about EPCs through ionotropic AChR and their effects on EPPs at the neuromuscular junction to the general case of chemical synapses between pairs of neurons. - -Instead of so called EPPs, the postsynaptic potentials between neurons we call excitatory if it increases the likelihood of an AP firing in a postsynaptic cell and inhibitory if it decr the probability of an AP occurring in a postsynaptic cell. - -This plot shows two pretend neurotransmitters D and H that can depolarize or hyperpolarize the cell and their corresponding Erevs. This one causes an EPSP and inward current from Vrest, whereas this one causes an IPSP and an outward current from Vrest. - ---- - ## Similar mechanisms exist at all chemical synapses -* Instead of end plate current called postsynaptic current (PSC). -* Instead of end plate potential called post synaptic potential (PSP). -* excitatory PSP– EPSP increases likelihood of an action potential -* inhibitory PSP– IPSP decreases likelihood of an action potential +For synapses between neurons: + +* Postsynaptic current (PSC) is similar to an end plate current +* Post synaptic potential (PSP) is similar to an end plate potential + * Excitatory PSP (EPSP)– increases likelihood of an action potential occurring + * Inhibitory PSP (IPSP)– decreases likelihood of an action potential occurring Note: +So now let's generalize the properties that we’ve learned about EPCs through ionotropic AChR and their effects on EPPs at the neuromuscular junction to the case of chemical synapses between any pair of neurons... + +But instead of the so called EPPs, we'll call the postsynaptic potentials between neurons we call excitatory PSP if it increases the likelihood of an AP firing in a postsynaptic cell and inhibitory PSP if it decr the probability of an AP occurring in a postsynaptic cell. + + + + + --- ## EPSP summation -* Unlike the neuromuscular junction– at synapses between neurons an EPSP is usually not very strong, usually well below threshold. What is needed is a bunch of EPSPs to sum together. Typically neurons receive more than a thousand synapses. It is basically the summation of EPSPs and IPSPs that determine whether or not an action potential occurs. If sum is above threshold, an AP happens. +* Unlike the neuromuscular junction– at synapses between neurons an individual EPSP is usually not very strong, typically well below threshold. +* Multiple EPSPs need to be summed together for the neuron's Vm to reach threshold. Individual neurons can receive thousands synapses. It's the summation of EPSPs and IPSPs that determine whether or not an action potential occurs. Note: @@ -338,143 +344,121 @@ Note: ## EPSP -* Here is an EPSP mediated by glutamate activating nonselective cation channels. + -Neuroscience 5e 5.21 +
EPSP mediated by glutamate activating nonselective cation channels
Neuroscience 5e Fig. 5.21
-
+Note: + +So imagine an experiment like we were doing before... + +--- + +## IPSP type 1 + +* Here is an IPSP mediated by GABA activating Cl⁻ selective channels +* The reversal potential for the Cl current is negative to the resting potential and threshold +* Activation of Cl channels hyperpolarizes the neuron + +
IPSP mediated by Cl⁻ selective ion channel
Neuroscience 5e Fig. 5.21
Note: --- -## IPSP #1 +## IPSP type 2 -* Here is an IPSP mediated by GABA activating Cl- selective channels. -* The reversal potential for the Cl current is negative to the resting potential and threshold. -* Activation of Cl channels hyperpolarizes the neuron. +* The reversal potential for the Cl⁻ current is positive to the resting potential but negative to threshold +* Activation of Cl⁻ channels depolarizes the neuron. Stabilizes membrane potential below threshold -ECl +
IPSP mediated by Cl⁻ selective ion channel
Neuroscience 5e Fig. 5.21
+
EPSP: Erev > thresh, IPSP: Erev< thresh
Neuroscience 5e Fig. 5.21
-Neuroscience 5e 5.21 - -Time (ms) Note: +Imagine if a separate EPSP input brought Vm of this neuron to -41 mV, just below -40mV threshold. Since this is now postive to the ECl of -50mV, further activity at the IPSP synapses will now hyperpolarize the neuron back towards -50mV. ---- +This can also be called shunting inhibition. In this case Na⁺ channels could persistently be in a state of inactivation due to small ongoing depolarizing and hyperpolarzing pulses keeping the neurons Vm below threshold. -## IPSP #2 - -* The reversal potential for the Cl– current is positive to the resting potential but negative to threshold. -* Activation of Cl– channels depolarizes the neuron. Stabilizes membrane potential below threshold. - -ECl - -Neuroscience 5e 5.21 - -Time (ms) - -Note: - - -Also called shunting inhibition. Na+ channels persistently in state of inactivation due to small depolarizing pulses. - -So just remember if the Erev for the neurotransmitter receptor is more positive than threshold than it is excitatory. If it is more negative than threshold than it is inhibitory. +So just remember, the key is that if the Erev for the neurotransmitter receptor is more positive than threshold than it is excitatory. If it is more negative than threshold than it is inhibitory. >Blocking NKCC1 with bumetanide disrupts excitatory synapse development in the cortex -Bumetanide, a selective NKCC1 inhibitor, has been demon- strated to suppress certain forms of epileptiform activity in vitro and in vivo, presumably by attenuating the depolarizing effect of GABA (Dzhala et al., 2005; Kilb et al., 2007) - - ->effect of GABA on membrane polarity depends on the Cl gradient created by the expression of Na -K -2Cl cotrans- porter (NKCC) and K -Cl cotransporter (KCC). NKCC1 im- ports Cl and is expressed from the embryonic stage until the first postnatal week, whereas KCC2 exports Cl and is weakly expressed at birth and upregulated as the brain matures (Plotkin et al., 1997; Rivera et al., 1999; Li et al., 2002). The temporal expression patterns of these two transporters correspond to the switch of GABA from being excitatory to inhibitory during the first few weeks of rodent postnatal life (Delpire, 2000). - ---- - -## Remember in neurons an EPSP is not driven from one pulse - -* Activation of ionotropic receptors opens nonselective cation channels. -* The first stimulation does not reach threshold. -* More intense stimulation yields a larger EPSP and an AP. - -
- -Note: - - ---- - -## IPSP - -* Activation of ionotropic receptors opens Cl- channels. -* The first stimulation does not reach threshold. -* More intense stimulation yields a longer IPSP but not a larger one. - -Note: +*Bumetanide, a selective NKCC1 inhibitor, has been demonstrated to suppress certain forms of epileptiform activity in vitro and in vivo, presumably by attenuating the depolarizing effect of GABA (Dzhala et al., 2005; Kilb et al., 2007)* +>effect of GABA on membrane polarity depends on the Cl gradient created by the expression of Na -K -2Cl cotransporter (NKCC) and K-Cl cotransporter (KCC). NKCC1 imports Cl and is expressed from the embryonic stage until the first postnatal week, whereas KCC2 exports Cl and is weakly expressed at birth and upregulated as the brain matures (Plotkin et al., 1997; Rivera et al., 1999; Li et al., 2002). The temporal expression patterns of these two transporters correspond to the switch of GABA from being excitatory to inhibitory during the first few weeks of rodent postnatal life (Delpire, 2000). --- ## Summation of postsynaptic potentials -Neuroscience 5e 5.22 - -
- -
+
Neuroscience 5e Fig. 5.22
+
Neuroscience 5e Fig. 5.22
Note: + --- ## Summation -* In general EPSPs in neurons are small 0.2–0.4 mV. -* Most neurons are somewhere between 10–20 mV below threshold. If everything was linear that it would take the sum of 50 or so inputs to trigger AP -* Not so simple. Some inputs are bigger than others, the inputs can be summed differently– spatially or temporally. -* A single neuron can have as many as 10,000 different synapses. Some excitatory some inhibitory, some strong some weak. Some at the tips of dendrites, some near the cell body. -* A neuron integrates all this information and either fires a spike or not. +* In general EPSPs in neurons are small 0.2–0.4 mV +* Most neurons are somewhere between 10–20 mV below threshold. If everything was linear that it would take the sum of 50 or so inputs to trigger AP +* Not so simple. Some inputs are bigger than others, the inputs can be summed differently– spatially or temporally +* A single neuron can have as many as 10,000 different synapses. Some excitatory some inhibitory, some strong some weak. Some at the tips of dendrites, some near the cell body +* A neuron integrates all this information and either fires a spike or not Note: Of course we are greatly simplifying everything here, a single neuron may have as many as 10K synaptic inputs. ---- - -## Neural integration - -
- -Note: - - --- ## Neural integration +
+
+ * How does a neuron integrate all the information it is getting? -* In most motor neurons and interneurons the decision to initiate an action potential is at the axon hillock. Contains a high density of voltage dependent Na+ channels. Contains membrane with lowest threshold. -* Axon hillock is senses the local state of the cell, which is the combination of all the EPSPs and IPSPs going on at one time. -* This is mostly due potentials that spread passively. -* Temporal summation, process by which consecutive synaptic potentials at the same site are added together. Different synapses will have different time constants. -* Length constant of the cell determines the degree to which a depolarization current decreases as it spreads passively. Easier to sum inputs on the same dendritic branch than on different branches. -* Some dendrites even have voltage gated Na+ channels, these can amplify inputs. +* In most motor neurons and interneurons the decision to initiate an action potential is at the axon hillock. Contains a high density of voltage dependent Na⁺ channels. Contains membrane with lowest threshold +* Axon hillock is senses the local state of the cell, which is the combination of all the EPSPs and IPSPs going on at one time +* This is mostly due potentials that spread passively +* Temporal summation, process by which consecutive synaptic potentials at the same site are added together. Different synapses will have different time constants +* Length constant of the cell determines the degree to which a depolarization current decreases as it spreads passively. Easier to sum inputs on the same dendritic branch than on different branches +* Some dendrites even have voltage gated Na⁺ channels, these can amplify inputs + +
Note: -some neurons in the globus pallidus have voltage gated Na channels. + + + + --- -## Title Text +## Summation of postsynaptic potentials video -[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation05-02SummationofPostsynapticPotentials.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation05-02SummationofPostsynapticPotentials.mov) - -
+
Neuroscience 5e Animation 5.2
Note: @@ -483,76 +467,20 @@ Note: ## Events from neurotransmitter release to postsynaptic excitation or inhibition -
+
Neuroscience 5e Fig. 5.23
Note: - ---- - -## Ionotropic neurotransmitter receptors - -Note: - -neurotransmitter binds - -channel opens - -ions flow across membrane - - ---- - -## Metabotropic neurotransmitter receptors - -Note: - -neurotransmitter binds - -g protein is activated - -g protein subunits or intracellular messengers modulate ion channels - -ion channel opens - -ions flow across membrane - - - ---- - -## Metabotropic neurotransmitter receptors - -Ligand binding site - -G-protein binding site - -
- -Note: - -neurotransmitter binds - -g protein is activated - -g protein subunits or intracellular messengers modulate ion channels - -ion channel opens - -ions flow across membrane - - - --- ## Cholinergic receptors * Best studied– the nicotinic ACh receptor (nAChR) -* Pentamer-5 subunits to make a pore. Selective for cations. -* Nicotine can mimic ACh to stimulate receptor, this is called an agonist. Most effects of nicotine go through this receptor. Nicotine is not cleared very well so receptor stays open longer which leads to larger EPSPs -* nACh receptors produce EPSPs. -* Many toxins specifically bind to and block nicotinic receptors called antagonists. -* alpha-bungarotoxin (snake venom)– binds to alpha subunit of nAChR very tightly and prevents ACh from activating it. +* Pentamer- 5 subunits to make a pore. Selective for cations +* Nicotine can mimic ACh to stimulate receptor, this is called an agonist. Most effects of nicotine go through this receptor +* nACh receptors produce EPSPs +* Many toxins specifically bind to and block nicotinic receptors called antagonists +* alpha-bungarotoxin (snake venom)– binds to alpha subunit of nAChR very tightly and prevents ACh from activating it Note: @@ -560,28 +488,35 @@ As we’ve shown in our examples earlier the nAChR receptor is a non-selective c 5 subunits ---- +*nAChR permeable to Na+, K+, and Ca2+* -## nAChR +from [#Picciotto:2000]: +>some subtypes of nAChR in the brain (those containing the b2 subunit) are located diffusely throughout the membrane of the neuron, with no obvious concentration at the synaptic junction (Hill et al. 1993). +a number of alpha and beta subunits have expression throughout brain (medulla, superior colliculus, cortex, beta2 subunit expression 'very high' in thalamus). Only alpha3 KO mice have high mortality [#Picciotto:2000]. + +[#Picciotto:2000]: Picciotto, M. R., Caldarone, B. J., King, S. L., and Zachariou, V. (2000). Nicotinic receptors in the brain. Links between molecular biology and behavior, Neuropsychopharmacology, 22(5), 451-65. PMID 10731620 + +Low (nM) concentrations of nicotine are found in the blood of moderate smokers (Henningfield et al. 1983). These are sufficient to enhance excitatory transmission in cultures of neurons from the medial habenula or the hippocampus (Gray et al. 1996; McGehee et al. 1995) [#Picciotto:2000] + +Many effects of nicotine probably through presynaptic or preterminal nAChRs instead of through postsynaptic AChRs (Léna et al. 1993; Marshall et al. 1997; McGe- hee et al. 1995; Summers and Giacobini 1995; Vidal and Changeux 1993; Wonnacott et al. 1990; Yang et al. 1996) [#Picciotto:2000] + + + --- ## Structure of the nACh receptor -* 5 subunits come together to make a pore. -* Each subunit has 3-4 membrane spanning domains. -* In muscles the receptor has 2 α, β,γ,ε subunits. The α subunits bind ACh, both need to be bound for channel to open. α subunits also binds bungarotoxin and nicotine. +* 5 subunits come together to make a pore +* Each subunit has 3-4 membrane spanning domains +* In muscles the receptor has 2α, β, δ, γ, ε subunits. The α subunits bind ACh, both need to be bound for channel to open. α subunits also binds bungarotoxin and nicotine * Multiple isoforms for each subunit, depending on which isoform is in channel get different properties -* In neurons its slightly different. 5 subunits 3α:2β. Bungarotoxin only inhibits muscle nACh receptors. +* In neurons its slightly different. 5 subunits 3α:2β. Bungarotoxin only inhibits muscle nACh receptors -
+
Neuroscience 5e Fig. 6.3
Note: @@ -591,14 +526,12 @@ The alpha subunits bind ACh. ## Muscle nAChR -* Pentamers of 2α1, ß1, γ, δ in fetal mammals vs. 2α1, ß1, δ, ε in adult mammal +* Pentamers of 2α1, β1, γ, δ in fetal mammals vs. 2α1, β1, δ, ε in adult mammal * ACh, nicotine, curare, and bungarotoxin binding sites are on the α1 subunits +* Pore diameter 10x bigger than Na⁺ channels (3 nm vs 0.3 nm) -Pore diameter 10x bigger than Na+ channels +
Neuroscience 3e 2001
-(3 nm vs .3 nm) - -
Note: @@ -609,96 +542,125 @@ curare is a competitive antagonist. --- -## Ligand Gated Ion Channels +## Ligand gated ion channels * Built up of 4 or 5 monomers * Each monomer spans the membrane 3 or 4 times * Each monomer contributes properties * Mixing and matching from a large pool of monomer isoforms creates receptors with different properties -
+
Neuroscience 3e 2001
+ Note: +Ligand gated channels in general are made up of 4 or 5 subunit monomers. + --- ## Muscarinic ACh receptors -
- -Note: - - ---- - -## Muscarinic ACh receptors - -* Muscarine, a poisonous mushroom alkaloid, is an agonist. -* Metabotropic, mediates most of ACh effects in the brain. +* Muscarine, a poisonous mushroom alkaloid, is an agonist +* Metabotropic (G-protein coupled receptors), mediates most ACh effects in the brain + * typically linked to K⁺ channel opening that results in IPSPs * 5 or so isoforms -* mACh blockers are used for pupil dilation (atropine), motion sickness (scopolamine) and asthma treatment (ipratropium). +* mAChR blockers are used for pupil dilation (atropine), motion sickness (scopolamine) and asthma treatment (ipratropium) + +
[*Amanita muscaria*, Onderwijsgek, CC BY-SA 3.0 nl](https://commons.wikimedia.org/w/index.php?curid=21983879)
+ +
Neuroscience 5e Fig. 6.4
+ Note: -- seven transmembrane spanning domains. +- seven transmembrane spanning domains - coupled to G proteins -- cause variety of slow postsynatpic responses. -- highly expr in sttiatum and varous forebrain regions. -- activate inward rectifier K+ channels (allow more K current at hyperpolarized potentials) -- or Ca2+ activated K+ channels +- causes variety of slow postsynatpic responses +- highly expr in striatum and varous forebrain regions +- activate inward rectifier K⁺ channels (allow more K current at hyperpolarized potentials) +- or Ca²⁺ activated K⁺ channels - exert inhibitory influence on dopamine mediated motor effects +- though in hippocampus mAChRs are excitatory, acting by closing KCNQ type K⁺ channels -in hippocampus mAChRs are excitatory, acting by closing KCNQ type K+ channels +*Also found in ganglia of PNS. Mediate peripheral cholinergic responses of autonomic effector organs like heart, smooth muscle, exocrine glands. Inhibition of heart rate by vagus nerve.* +* KCNQ... * mutations in four out of five KCNQ genes underlie diseases including cardiac arrhythmias, deafness and epilepsy. * [http://www.ncbi.nlm.nih.gov/pubmed/11252765](http://www.ncbi.nlm.nih.gov/pubmed/11252765) * KCNQ/M (Kv7) very slow voltage-gated K channels, suppress repetitive firing * Inhibited by ACh and many neurotransmitters, but enhanced by others -* [http://physiolgenomics.physiology.org/content/22/3/269](http://physiolgenomics.physiology.org/content/22/3/269) +* [http://physiolgenomics.physiology.org/content/22/3/269](http://physiolgenomics.physiology.org/content/22/3/269) -Also found in ganglia of PNS. Mediate peripheral cholinergic responses of autonomic effector organs like heart, smooth muscle, exocrine glands. Inhibition of heart rate by vagus nerve. +atropine +: from deadly nightshade family +: dilate pupils, treat slow heart rate +: anticholinergic, muscarinic antagonist +: inhibits parasympathetic nervous system +: WHO essential medicine ---- +scopolamine +: colorless, odorless alkaloid drug +: competitive antagonist, antimuscarinic +: motion sickness, postoperative nausea and vomiting +: WHO essential medicine +: from flowering plant genus *Scopolia* -## Muscarinic ACh receptors +ipratropium +: opens up medium and large airways of lungs by causing smooth muscles to relax +: anticholinergic and muscarinic antagonist +: treats obstructive pulmonary disease and asthma +: WHO essential medicine -* Muscarine, a poisonous mushroom alkaloid, is an agonist. -* Metabotropic, mediates most of ACh effects in the brain. -* 5 or so isoforms -* mACh blockers are used for pupil dilation (atropine), motion sickness (scopolamine) and asthma treatment (ipratropium). -* [Also used for bad things http://www.rense.com/general38/frug.htm](http://www.rense.com/general38/frug.htm) - -Note: +*Clitocybe dealbata* +: muscarine can occur in this species sufficient concentrations to be deadly +: commonly found growing in lawns in North America an Europe +: white flat topped + [*Amanita muscaria*, Onderwijsgek, CC BY-SA 3.0 nl](https://commons.wikimedia.org/w/index.php?curid=21983879) + : red mushroom with white speckles + : muscarine first isolated from this species in 1869 + : muscarine actually only in trace amounts in this species + : muscimol is a predominent compound from this mushroom though --- ## Glutamate receptors * Both ionotropic and metabotropic -* Ionotropic– NMDA receptors, AMPA receptors, and Kainate receptors (named after the agonists that stimulate them). -* All are non-selective ion channels with Erev close to 0 (above threshold therefore excitatory). -* Formed from an association of many subunits, that can combine to create many isoforms. +* Ionotropic– AMPA/Kainate receptors and NMDA receptors (named after the agonists that stimulate them) + * All are non-selective ion channels with Erev close to 0 (above threshold therefore excitatory) + * Formed from an association of 4 subunits. There are a variety of possible subunits which can combine to create many receptor isoforms Note: -tetramers - -3 classes, 8 subunits - -Kainate receptors, or KARs, are ionotropic receptors that respond to the neurotransmitter glutamate. - -Kainic acid (kainate) is a natural marine acid present in some seaweed. Kainic acid is a potent neuroexcitatory amino acid that acts by activating receptors for glutamate, +* form tetramers +* ??*3 classes, 8 subunits*?? +* Kainate receptors, or KARs, are ionotropic receptors that respond to the neurotransmitter glutamate. +* Kainic acid (kainate) is a natural marine acid present in some seaweed. Kainic acid is a potent neuroexcitatory amino acid that acts by activating receptors for glutamate, * Domoic acid is a structural analog of kainic acid and proline. * Domoic acid (DA) is a kainic acid analog neurotoxin that causes amnesic shellfish poisoning --- -## Glutamate receptors +## Glutamate receptor subunit types -
+
+
+ +AMPA | Kainate | NMDA | Metabotropic +----- | ------- | ------- | ---------- +GluR1 | GluR5 | NR1 | mGluR1 +GluR2 | GluR6 | NR2A | mGluR5 +GluR3 | GluR7 | NR2B | mGluR2 +GluR4 | KA1 | NR2C | mGluR3 + | KA2 | NR2D | mGluR4 + | | NR2D | mGluR6 + | | NR3A | mGluR7 + | | NR3B | mGluR8 + +
Note: @@ -706,218 +668,160 @@ Note: ## AMPA/Kainate receptors -* glutamate receptors that allow Na+ or K+ ions across. -* multi-subunit channels +* ionotropic glutamate receptors that allow Na⁺ or K⁺ ion flow +* multi-subunit channels (typically as heterotetramers from a pair of GluR2 plus a pair of GluR1, GluR3, or GluR4) * evoke EPSPs that are large and fast * AMPA receptors are more common than Kainate receptors -
+
Neuroscience 5e Fig. 6.6
Note: +* Each AMPAR is composed of 4 subunits and has four sites to an agonist like glutamate can bind (one per subunit) +* alternative splicing of each of the 4 subunit genes can result in a number of more isoforms +* GluR1 and GluR2 especially important in synaptic plasticity by being upregulated + --- ## NMDA receptor -* Glutamate receptors that allow flow of Ca2+ as well as Na+ and K+. As a result EPSPs produced by NMDA receptors can increase the Ca2+ concentration in the neuron. Acts as a second messenger to activate cellular processes. +
+
+ +* Glutamate receptors that allow flow of Ca²⁺ as well as Na⁺ and K⁺. As a result EPSPs produced by NMDA receptors can increase the Ca²⁺ concentration in the neuron. Acts as a second messenger to activate cellular processes +* Formed as a heterotetramer of 4 subunits (typically 2 NR1 and 2 NR2 subunits) * Needs a co-agonist, glycine to open channel -* Blocked by Mg2+ in the pore during hyperpolarizing conditions. Depolarization can remove block. Needs either a bunch of presynaptic cells to fire at the same time or repeated firing of presynaptic cell to open channel. -* Key component of a model for learning. -* Evoke EPSPs that are slow and long lasting. -* PCP “angel dust” binds and clogs channel. Get symptoms similar to schizophrenia. +* Blocked by Mg²⁺ in the pore during hyperpolarizing conditions. Depolarization can remove block. Needs either a bunch of presynaptic cells to fire at the same time or repeated firing of presynaptic cell to open channel +* Key component of a model for learning +* Evoke EPSPs that are slow and long lasting +* PCP “angel dust” binds and clogs channel. Get symptoms similar to schizophrenia + +
Note: -PCP “angel dust” binds and clogs channel. Get symptoms similar to schizophrenia. Some hypothesize NMDA receptor is involved in this disease. +* NR1 has the glycine agonist binding site +* NR2 has the glutamate binding site +* NR2B predominant in developing brain before switching to NR2B being predominant in adults +* PCP “angel dust” binds and clogs channel. Get symptoms similar to schizophrenia. Some hypothesize NMDA receptor is involved in this disease. --- -## NMDA receptor currents requires glutamate, glycine, and removal of voltage-gated Mg2+ block +## NMDA receptors require removal of a voltage-dependent Mg²⁺ block -* Glycine is a co-agonist-no glycine no current. -* Mg2+ blocks pore-is removed by depolarization. -* This can happen because AMPA and NMDA receptors are often in the same synapse. +
+
-Neuroscience 5e 6.6 +* Mg²⁺ blocks pore– removed by depolarization +* This is possible because AMPA and NMDA receptors are often at the same synapse + +
+ +
Neuroscience 5e Fig. 6.6
-
Note: - + --- -## NMDA receptor currents require glycine and removal of Mg2+ block +## NMDA receptors can open only during depolarization -
+
Neuroscience 5e Fig. 8.10
-Note: - -fig from: - -[http://www.bris.ac.uk/synaptic/info/glutamate.html](http://www.bris.ac.uk/synaptic/info/glutamate.html) - ---- - -## The NMDA receptor channel can open only during depolarization - -
Note: chp 8 more on NMDA-R mediated mechanisms involved in learning and memory, adv neuroscience. - --- -## Building a brainier mouse - -* NMDA receptor consists of four subunits, each constructed separately. -* Receptors with NR2B subunits stay open longer than those with NR2A. -* Genetically engineered mice to produce NR2B receptors, the DOOGIE mouse. -* The genetically engineered mice showed stronger synaptic connections, faster fear learning, and better water maze learning. - -Tsien, J.Z (2000) Building a brainier mouse. - -Scientific American, April , Vol 282, pp62-68. - -
- -
- -Note: - -Conductances during early infancy and as an adult - ---- - -## Neurobiology: Young receptors make smart mice - -Figure 1 Object-recognition task. a, In an initial training session the mouse explores two - -objects in a box, devoting roughly equal time to each. - - b, When the mouse is then re-exposed to one of these objects, together with a new object, - - it spends more time exploring the new object. Tang et al.3 find that this bias is enhanced in - -transgenic mice (inset) over expressing the NR2B - -subunit of the NMDA receptor, indicating improved recognition memory. - -subunit NR2A in adults subunit NR2B during development - -
- -Note: - - ---- - -## Metabotropic glutamate receptors mGluRs +## Metabotropic glutamate receptors (mGluRs) * Large class of receptor subtypes * G-protein coupled -* Often leads to inhibition of postsynaptic Ca2+ and Na+ channels +* Often leads to inhibition of postsynaptic Ca²⁺ and Na⁺ channels * But sometimes inhibitory sometimes excitatory Note: +* group I (mGluR1, mGluR5) associated with IP3 signaling and ER Ca2+ channel opening. Also associated with Na+ and K+ channels. Can result in EPSPs but can also result in IPSPs. + * activated selectively by 3,5-dihydroxyphenylglycine (DHPG) (but not other groups) +* group II mGluRs 2 and 3 prevent formation of cAMP (by activating Gi that inhibits adenylyl cyclase) and result in presynaptic inhibition (not apparently affecting PSPs directly) +* group III, including mGluRs 4, 6, 7, and 8 prevent formation of cAMP and have similar functional pathway and consequences as group II --- ## GABA receptors -* Three types of GABA receptors: A, B and C. -* A and C are ionotropic, B is metabotropic. -* A and C are inhibitory because their channels are permeable to Cl-. The flow of Cl- into the cell lowers the potential. Erev is less than the threshold potential. -* Pentamers, subunit diversity as well as variable stoichiometry, allows for variable functions of GABA receptors. -* Glycine receptors have generally the same properties as GABA receptors +* Three types of GABA receptors: A, B and C +* A and C are ionotropic, B is metabotropic +* A and C are inhibitory because their channels are permeable to Cl⁻. The flow of Cl⁻ into the cell lowers the potential. Erev is less than the threshold potential +* Pentamers, subunit diversity as well as variable stoichiometry, allows for variable functions of GABA receptors +* Glycine receptors generally have the same properties as GABA receptors Note: -\pentameric +* pentameric +* GABAB metabotropic receptors always inhibitory. Coupled indirectly to K+ channels and can decreased Ca2+ conductance resulting in less cAMP production. Baclofen is a potent and selective GABAB agonist. GABA responses that are insensitive to bicuculline and baclofen are termed GABAC responses. +* GABAA: muscimol potent agonist from mushrooms. Bicuculline classical antagonist and convulsant. --- ## Ionotrophic GABA Receptors -
+
Neuroscience 5e Fig. 6.9
Note: -In this example Erev>Vm so chloride goes from - -inside to outside - -[from: https://en.wikipedia.org/wiki/Picrotoxin](https://en.wikipedia.org/wiki/Picrotoxin) - -picrotoxin +[picrotoxin](https://en.wikipedia.org/wiki/Picrotoxin) >Found primarily in the fruit of the climbing plant Anamirta cocculus, it has a strong physiological action. It acts as a non-competitive channel blocker for the GABAA receptor chloride channels.[3] It is therefore a channel blocker rather than a receptor antagonist. --- -## Ionotrophic GABA Receptors +## Examples of IPSPs recorded at different membrane potentials -current due to many channels +
Erev is at the Nernst potential for Cl⁻ (e.g. –80 mV)
Coombs et al., J Physiol 1955 Fig. 1
-opening - -step nature shows individual - -channels closing. - -In this example Erev>Vm so Cl– goes from - -inside to outside - -
Note: -In this example Erev>Vm so chloride goes from +Coombs, Eccles, Fatt 1955: double barreled pipete, inject small currents through one barrel (for voltage clamp) in biceps motorneuron (crustacean) to hold Vm while stimulating afferent nerve inputs to get IPSPs. Erev was found to be close to ECl. Notice hyperpolarization when Vm was above -78 mV, small depolarizations when Vm below -80mV. They found that messing with Cl- concentrations would correspondingly alter the IPSPs but not when messing with Na or K concentrations. Thus Cl- ion flux is necessary for the IPSPs. -inside to outside +[#Coombs:1955]: Coombs, J. S., Eccles, J. C., and Fatt, P. (1955). The specific ionic conductances and the ionic movements across the motoneuronal membrane that produce the inhibitory post-synaptic potential, J Physiol, 130(2), 326-74. PMID 13278905 ---- - -## Examples of GABA receptor-mediated IPSPs recorded at different membrane potentials - -Reversal potential is at the Nernst potential for Cl- ions. - -(In this case about –78 mV) - -Figure from Coombs et al. 1955) - -
- -Note: --- -## GABA induced IPSPs +## Ionotropic GABA receptor mediated IPSPs -Stimulate GABA producing interneuron- record from post-synaptic neuron +
Stimulate GABA producing interneuron, record from post-synaptic neuron
Neuroscience 5e Fig. 6.9
-
Note: +Chavas and Marty performed Gramacidin perforated patch recordings from young rat cerebellum interneurons and purkinje cells. *Interneurons had more depolarized GABAA reversal potentials than purkinje cells at matched ages (e.g. P12, likely from higher [Cl-]intra for interneurons compared to purkinje cells).* + +[#Chavas:2003]: Chavas, J. and Marty, A. (2003). Coexistence of excitatory and inhibitory GABA synapses in the cerebellar interneuron network, J Neurosci, 23(6), 2019-31. PMID 12657660 + --- -## The GABA receptor binds many interesting things +## GABA receptors bind many interesting things -[http://www.youtube.com/watch?v=L6dzUOYTQtQ-](http://www.youtube.com/watch?v=L6dzUOYTQtQ-) +
A Biologist's St. Patrick's Day Song
+ +
Basic Neurochemistry 6e Fig. 16.2
-
Note: +Start at around 1:23 + [from: https://en.wikipedia.org/wiki/Barbiturate#Mechanism_of_action](https://en.wikipedia.org/wiki/Barbiturate#Mechanism_of_action) >Barbiturates act as positive allosteric modulators, and at higher doses, as agonists of GABAA receptors. @@ -930,7 +834,7 @@ Note: [from: http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_alcool.html](http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_alcool.html) ->GABA’s effect is to reduce neural activity by allowing chloride ions to enter the post-synaptic neuron. These ions have a negative electrical charge, which helps to make the neuron less excitable. This physiological effect is amplified when alcohol binds to the GABA receptor, probably because it enables the ion channel to stay open longer and thus let more Cl- ions into the cell. +>GABA’s effect is to reduce neural activity by allowing chloride ions to enter the post-synaptic neuron. These ions have a negative electrical charge, which helps to make the neuron less excitable. This physiological effect is amplified when alcohol binds to the GABA receptor, probably because it enables the ion channel to stay open longer and thus let more Cl⁻ ions into the cell. >Still other substances block a natural neuromediator. Alcohol, for example, blocks the NMDA receptors. @@ -940,10 +844,10 @@ Note: ## Serotonin receptors -* Large family of receptors called 5-HT 1-7. -* 5-HT3 is a ligand gated non-selective cation channel, thus it is excitatory. -* Same basic structure as nACh receptor. -* All others are metabotropic– likely that perturbations in these receptors are involved in many neural disorders. +* Large family of receptors called 5-HT 1-7 +* 5-HT3 is a ligand-gated non-selective cation channel, thus it is excitatory + * Same basic structure as nACh receptor +* All others are metabotropic– likely that perturbations in these receptors are involved in many neural disorders Note: @@ -953,10 +857,10 @@ most receptors are metabotropic ## Catecholamine receptors -* Act exclusively by activating G-protein coupled receptors. Contribute to complex behaviors. -* Norepinephrine and epinephrine each act on α and β adrenergic receptors. -* Mostly used to control smooth muscles, especially cardiovascular. -* B-blockers are used to treat hypertension, anxiety, and panic. +* Act exclusively by activating G-protein coupled receptors. Contribute to complex behaviors +* Norepinephrine and epinephrine each act on α and β adrenergic receptors +* Mostly used to control smooth muscles, especially cardiovascular +* B-blockers are used to treat hypertension, anxiety, and panic Note: @@ -965,13 +869,13 @@ Note: ## Peptide receptors -* Virtually all mediate their effects by activating G-protein coupled receptors. -* Neuropeptide-Y receptor important in food intake/ obesity. -* Opiate receptors have been identified and shown to be important in addiction (e.g. µ-opioid receptor). +* Virtually all mediate their effects by activating G-protein coupled receptors +* Neuropeptide-Y receptor important in food intake/obesity +* Opiate receptors have been identified and shown to be important in addiction (e.g. µ-opioid receptor) Note: -Opioid peptides distributed throughout the brain. Colocalize with GABA and 5-HT. Tend to be depressants. They act like analgesics when injected intracerebrally. Initiate effects through GPCRs. Activate at low concentrations (nM to uM). mu, delta, kappa opioid receptor subtypes play role in reward and addiction. mu-receptor is primary site for opiate drugs. +Opioid peptides distributed throughout the brain. Colocalize with GABA and 5-HT. Tend to be depressants. They act like analgesics when injected intracerebrally. Initiate effects through GPCRs. Activate at low concentrations (nM to uM). mu, delta, kappa opioid receptor subtypes play role in reward and addiction. mu-receptor is primary site for opiate drugs. --- @@ -980,39 +884,27 @@ Opioid peptides distributed throughout the brain. Colocalize with GABA and 5-HT. * ATP is contained in all synaptic vesicles * Has specific receptors on post-synaptic cells -* P2X -* A2A adenosine receptor (blocked by caffeine) + * P2X + * A2A adenosine receptor (blocked by caffeine) * Generally excitatory in nature -* Used in spinal cord, motor neurons, and other ganglia. +* Used in spinal cord, motor neurons, and other ganglia Note: -Another neurotransmitter that we didn’t talk about last time is +Another neurotransmitter that we didn’t talk much about last time is Receptors for ATP and adenosine are widely distributed through the nervous system as well as other tissues. One class of purinergic receptors for ATP and adenoscie are P2X-receptors which are ionotropic non-selective cation receptors. Others are GPCRs like A2A adenosine receptor throughout brain and heart, adipose tissue, and kidney. Xanthines like caffeine and theophylline block adenosine receptors and this is thought to be the cause of its stimulant effects. - - ---- - -## Title Text - -
- -
- -Note: - --- ## Summary -* Neurotransmitter receptors bind neurotransmitters. Tremendous diversity but with commonalities. -* Two types– ionotropic (ligand-gated ion channel) and metabotropic (G-protein coupled receptor). -* Both types lead to opening or closing of ion channels. These conductance changes can either increase or decrease the probability of firing an action potential. -* Because postsynaptic neurons are usually innervated by many different inputs, it is the combination of EPSP and IPSPs that determines whether a cell fires and if an action potential occurs. +* Neurotransmitter receptors bind neurotransmitters. Tremendous diversity but with commonalities +* Two types– ionotropic (ligand-gated ion channel) and metabotropic (G-protein coupled receptor) +* Both types lead to opening or closing of ion channels. These conductance changes can either increase or decrease the probability of firing an action potential +* Because postsynaptic neurons are usually innervated by many different inputs, it is the combination of EPSP and IPSPs that determines whether a cell fires and if an action potential occurs Note: diff --git a/2016-10-16-lecture09.md b/2016-10-16-lecture09.md new file mode 100644 index 0000000..b468ef6 --- /dev/null +++ b/2016-10-16-lecture09.md @@ -0,0 +1,621 @@ +## Signal transduction + +* Neurons can change their state (e.g. which receptors, channels, neurotransmitters are opened, modulated, or expressed) depending on what is going on in their local environment +* They receive signals from other neurons (neurotransmitters) and other cells (hormones, growth factors, and trophic factors) +* They have specialized machinery that can transduce these signals to changes in their physiological state. + +Note: + +Today we take a broad overview of signal transduction pathways that work to change the physiological state of neurons. Many of the pathways and second messengers should be familiar to you from basic cell biology. + +* hormones, estradiol, testosterone & (LH, FSH, progesterone) + +--- + +## Different types of cell-cell communication + +* Synaptic signaling +* Paracrine signaling– acts over a short range +* Endocrine signaling– secretion of hormones into the blood stream +* Membrane protein signaling– two cells next to each other signal through closely associated membrane proteins + +Note: + +What types of cell-cell communication underly signaling? The answer is familiar ones like… + +--- + +## Endocrine signaling + +
+ +Note: + +--- + +## Paracrine signaling + +
+ +Note: + +--- + +## Signaling by membrane proteins + +
+ +Note: + + +--- + +## Components of signaling + +* Signal (the message) +* Receptor (signal detection) +* Effector/target molecules (mediate the cellular response) +* Intracellular signal transduction refers to the events between the receptor and the effector targets +* Signal amplification often occurs during signal transduction + +Note: + + + +--- + +## Signal amplification + +* results in a tremendous increase in the potency of the initial signal +* permits precise control of cell behavior + +
+Note: + + +--- + +## Types of receptors + +* Ligand gated ion channels (channel linked receptors/ionotropic receptors)– e.g. nAChR, AMPA receptors +* Enzyme linked receptors– typically have extracellular binding site for signals. Has intracellular domain with catalytic activity regulated by signal. Most are protein kinases that phosphorylate intracellular proteins. e.g. tyrosine kinase +* G-protein coupled receptors– 7-transmembrane spanning receptors that signal through trimeric G-proteins intracellularly. The proteins can alter the function of many downstream proteins. e.g. muscarinic AChR, metabotropic glutamate receptors +* Intracellular receptors– activated by cell permeant or lipophilic signaling molecules like steroid hormones. Signal binds directly to an intracellular protein which then activates transcription + +Note: + + + +--- + +## Categories of cellular receptors + +Neuroscience 5e 7.4 + +
+ +Note: + +We already know how ion channels work. + +For enzyme linked receptors the signal binds extracellularly, which activates the intracellular enzymatic domain of the same protein catalyzing the production of a product from a substrate. + +--- + +## Categories of cellular receptors + +Neuroscience 5e 7.4 + +Note: + +For g protein coupled receptors, the signal binds to the receptor, then the g-protein binds and becomes activated. + +For intracellular receptors, the signaling molecule passes through lipid membrane, binds to the intracellular receptor and activates the receptors which can then enter the nucleus to regulate transcription. + + +--- + +## Downstream of activated receptors: G-proteins + +* G-proteins– GTP binding proteins +* G-proteins generally couple the active receptor to downstream targets. Called G-proteins because they hydrolyze GTP +* Two types of G-proteins: + * Heterotrimeric G- proteins, composed of an α,β, γ subunits. Multiple members of each class. α subunit binds and hydrolyses GTP + * Small G-proteins– monomeric GTPases (e.g. ras) +* Active when bound to GTP, inactive when bound to GDP. + +Note: + +G proteins couple receptor activation to downstream effects for G-protein coupled receptors. + +They hydrolyze guanine triphosphate to guanine diphosphate so that downstream proteins can become phosphorylated and activated. + +There are two types… + +heterotrimeric composed of three distinct subunits. It is the alpha subunit that binds to the guanine nucleotides GDP and GTP. + +binding of GDP allows the alpha subunit to bind to the beta and gamma subunits to form an inactive trimer. Binding of the extracellular signal to the receptor allows the g-protein to bind the receptor and GDP to be replaced with GTP. Then the alpha subunit with GTP is free to dissociate from the trimer and bind downstream effector molecules to mediate a host of responses inside the cell. + +The monomeric GTPases also relay signals from membrane receptors to intracellular targes like the cytoskeleton. Ras is the first small G protein discovered (rat sarcoma tumors). Helps regulated cell differentiation and proliferation, relaying signals from receptor kinases. + +Rate of GTP hydrolysis is important property of G-protein mediated signaling and can be regulated by proteins like GAPs (or GTPase activating proteins) that replace GTP with GDP to return G proteins to their inactive form. + +* - Guanosine-5'-triphosphate (GTP) is a purine nucleoside triphosphate. +* - Effector enzymes for activated G-proteins include adenylyl cyclase, guanylyl cyclase, phospholipase C, and others. +* - In some cases G-proteins can directly modulate ion channels. mAChR that slow heart rate from vagus nerve stimulation are thought to be due to beta/gamma G protein subunits binding to and modulating K channels. Alpha subunits of g proteins can lead to rapid closing of voltage-gated Ca and Na channels. + +--- + +## Types of GTP-binding proteins + +
+ +Note: + + + +--- + +## Trimeric G-protein signaling + +* Ligand binds receptor +* α subunit binds activated receptor +* GTP exchanged for GDP +* Dissociates complex and activates +* α and βγ subunits + +
+ +Note: + + + +--- + +## Downstream targets of G-proteins + +* Ion channels– can be directly-activated by both the βγ subunits (can gate some types of K⁺ channels) or by α subunits (can cause closing of voltage sensitive Na⁺ and Ca²⁺ channels) +* Enzymes that produce 2nd messengers– e.g. adenylyl cyclase, guanylyl cyclase, and phosopholipases +* Each 2nd messenger does different things +* Wide diversity of physiological responses + +Note: + +In some cases G-proteins can directly modulate ion channels. mAChR that slow heart rate from vagus nerve stimulation are thought to be due to beta/gamma G protein subunits binding to and modulating K channels. Alpha subunits of g proteins can lead to rapid closing of voltage-gated Ca and Na channels. + +Effector enzymes for activated G-proteins include adenylyl cyclase, guanylyl cyclase, phospholipase C, and others. + + +--- + +## Effector pathways associated with G-protein coupled receptors + +
+ +Note: + + +There are many types of alpha, beta, and gamma g-protein subunits allowing a specific and diverse range of downstream responses. + +This shows three examples of different heterotrimeric g proteins bound to 3 types of receptors with 3 different cellular responses. + + +--- + +## Second messengers: calcium + +* Maintained at low concentrations inside cytosol +* Binds to many proteins and regulates their activity +* Calmodulin– binds Ca²⁺ and then can activate calmodulin dependent protein kinases +* IP3 receptors– channel that lets calcium out of ER + +Note: + + +Maybe the most common intracellular messenger in neurons. + +One target of calcium is calmodulin, a calcium binding protein abundant in the cytosol of all cells. Calcium binding to this protein initiates downstream effects by binding to targets like protein kinases. + + +--- + +## Proteins involved in delivering and removing calcium to the cytoplasm + +
+ +Note: + +ATPase called the calcium pump (Ca-proton pump). Works on cell membrane and also pumps calcium into intracellular organelles like ER and mitochondria. + +Na/Ca exchanger that replaces intracellular Ca with extracellular sodium ions. + +VGCCs + +calcium binding effector proteins like calmodulin mediate downstream effectors of calcium. + +calcium binding buffer proteins serve as calcium buffers (calbindin, common in strongly expressed in some neuron subtypes). Can blunt the magnitude and kinetics of calcium signals. + +Channels that allow Ca to be released from the the interior of the ER like the inositol trisphosphate receptors (IP3). These are regulated by IP3, a second messenger. + +Another one intracellular releasing channel is the ryanodine receptor. These are activated by cytoplasmic Ca and for at least muscle cells, membrane depolarization. + + +--- + +## Calcium activates calmodulin + +
+ +Note: + + + +--- + +## Title Text + +[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation07-02CalciumasaSecondMessenger.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation07-02CalciumasaSecondMessenger.mov) + +
+ +Note: + + + +--- + +## Second messengers: cyclic nucleotides + +* cAMP and cGMP– derivatives of ATP and GTP. Made by adenylyl cyclase and guanylyl cyclase +* Bind to many targets– cAMP to protein kinase A; cGMP to protein kinase G +* Phosphodiesterases cleave cAMP and cGMP to inactivate them + +Note: + + + +--- + +## cAMP formation and destruction + +
+ +Note: + + + +--- + +## Second messengers: diacylglycerol and IP3 + +* Formed from the cleavage of lipids (phosphatidylinositols) by phospholipase C +* Diacylglycerol (DAG) activates protein kinase C +* IP3 opens calcium channels + +Note: + + + +--- + +## Diacylglycerol and IP3 + +
+ +Note: + +Phosphatidylinositol 4,5-bisphosphate: PIP2, + + +--- + +## Neuronal second messengers + +
+ +Note: + +This table summarizes neuronal second messengers, their sources, targets, and inactivation mechanisms. + + +--- + +## Second messenger life cycles + +cyclic nucleotides + +lipid signals + +Neuroscience 5e 7.7 + +
+ +
+ +Note: + +And this depicts the mechanisms involved in production and degradation or removal of cyclic nucleotides and DAG and IP3. + + +--- + +## Second messenger life cycles + +cyclic nucleotides + +lipid signals + +gas signals + +
+ +Note: + + +--- + +## 2nd messengers target protein kinases and phosphatases + +* Phosphorylation can rapidly alter a protein’s activity +* Phosphorylation is carried out by protein kinases and usually occurs on Ser/thr and tyr residues +* Dephosphorylation is carried out by protein phosphatases +* 2nd messengers typically activate Ser/Thr kinases +* Extracellular signals (e.g. growth factors) activate Tyr kinases + +Note: + +Second messengers regulate neuronal functions by modulating the phosphorylation of intracellular proteins. This addition and removal of phosphate groups rapidly and reversibly modulates protein function. + +Phosphorylation is carried out by protein kinases. + +Phosphate groups are removed by phosphatases. + +Protein substrates of kinases and phosphataes include enzymes, neurotransmitter receptors, ion channels, structural proteins. + + +--- + +## Regulation of cellular proteins by phosphorylation + +
+ +Note: + + + +--- + +## Ser/thr kinases + +* PKA– cAMP dependent protein kinase. Ser/thr kinase. Tetramer of 2 regulatory and 2 catalytic subunits. cAMP binds the regulatory subunits causing the release of catalytic subunits +* CaMKII– Ca²⁺/calmodulin-dependent protein kinase. Ser/thr kinase, very abundant in brain. 12 or so subunits. Downstream targets: many ion channels, other signal transduction proteins, tyrosine hydroxylase. Thought to be involved in learning/memory +* PKC– Ser/thr kinase activated by DAG and Ca²⁺. DAG causes PKC to move from the cytosol to the membrane where it binds Ca²⁺ and gets activated + +Note: + + + +--- + +## Mechanism of activation of protein kinases + +binding of cAMP to regulatory + +subunits free up the catalytic subunits + +binding of calmodulin opens up + +protein to activate catalytic domain + +DAG causes PKC to change its + +localization which leads it to be active + +
+ +Note: + + + +--- + +## Protein kinase A activation + +
+ +Note: + + + +--- + +## Other kinases + +* Protein tyrosine kinases– Two types receptor tyrosine kinases (Eph receptors, growth factor receptors) and cytoplasmic kinases (many oncogenes). Cytoplasmic tyrosine kinases are particularly important for cell growth and differentiation +* MAP kinases– mitogen activated kinases. Are often intermediate kinases, become activated by kinases and kinase other proteins. Often found downstream of receptor tyrosine kinases + +Note: + +Mitogen activated protein kinases (MAP kinases) + +* first identified as having a role in cell growth +* also called extracellular signal regulated kinases (ERKs). +* normally inactive in neurons, but activated when phosphorylated by other kinases +* part of kinase cascades. +* activation can be triggered by extracellular growth factors that bind receptor tyrosine kinases that activate monomeric G proteins like ras. +* can phosphorylate transcription factors + +--- + +## MAP kinase cascade + +
+ +Note: + + +--- + +## Nuclear signaling + +* Sometimes 2nd messengers (e.g. cAMP) can go into the nucleus where they can change the transcription of genes +* Transcription factors are proteins that interface with RNA polymerase to select promoter regions of genes +* These transcription factors can be regulated by phosphorylation + +Note: + +CREB is an important nuclear signal + +* [from https://en.wikipedia.org/wiki/Estrogen_receptor:](https://en.wikipedia.org/wiki/Estrogen_receptor) +* >estrogen receptors are largely located in the cytosol. Hormone binding to the receptor triggers a number of events starting with migration of the receptor from the cytosol into the nucleus, dimerization of the receptor, and subsequent binding of the receptor dimer to specific sequences of DNA known as hormone response elements. + + +--- + +## Steps involved in transcription of DNA to RNA + +
+ +Note: + +uas: upstream activator sequence + +[from https://en.wikipedia.org/wiki/Upstream_activating_sequence:](https://en.wikipedia.org/wiki/Upstream_activating_sequence) + +>upstream activating sequence or upstream activation sequence (UAS) is a cis-acting regulatory sequence. It is distinct from the promoter and increases the expression of a neighbouring gene. + +-upstream from minimal promoter TATA box, binding site for transactivators + +-a cis acting regulatory sequence (like IRES) + + +--- + +## CREB + +* CREB (cAMP response element binding protein). An important transcription factor +* Normally bound to DNA but not active. Phosphorylation activates it and it activates transcription. CREB is important for transcription of tyrosine hydroxylase, neuropeptides, neurotrophins and channel proteins +* Important for learning and memory, mothering instincts, synaptic plasticity + +Note: + +--- + +## Transcriptional regulation by CREB + +
+ +Note: + + +--- + +## Title Text + +[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation07-01ChemicalSignalingMechanismsandAmplification.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation07-01ChemicalSignalingMechanismsandAmplification.mov) + +
+ +Note: + + +--- + +## Nurturing defects in CREB mutant mice + +WT + +mutant + +
+ +Note: + + +--- + +## How does NGF promote axon outgrowth + +-NGF + ++NGF + +
+ +Note: + + + +--- + +## Mechanism of action of NGF + +
+ +Note: + + +nerve growth factor, binds to tyrosine kinase receptor (TrkA) leading to… + +--- + +## Signaling at cerebellar parallel fiber synapses + +* Glutamate released from presynaptic cell binds ionotropic and metabotropic glutamate receptors +* AMPA receptor opens and excites cell +* mGluR receptor activates a signal transduction pathway that feeds back and decreases AMPA receptor activity +* Called long term depression because now the same stimulus will lead to less depolarization than before (weakened synapse) + +
+ +Note: + +Can result from strong synaptic stimulation at cerebellar purkinje neurons or from weak synaptic stimulation in the hippocampus. + +* Both parallel fibers and climbing fibers must be simultaneously activated for LTD to occur. With respect to calcium release however, it is best if the parallel fibers are activated a few hundred milliseconds before the climbing fibres. + +LTD is thought to result mainly from a decrease in postsynaptic receptor density, + +likely from phosphorylation of AMPA receptors by PKC and their elimination from the synapse and involves mapk cascade + +* Hippocampal/cortical LTD can be dependent on NMDA receptors, metabotropic glutamate receptors (mGluR), or endocannabinoids.[4] +* LTP involves + + +--- + +## Regulation of tyrosine hydroxylase by protein phosphorylation + +* AP invades axon terminal +* Voltage-gated Ca²⁺ channels open +* Intracellular Ca²⁺ does two things: +* Short term causes vesicle fusion +* Long term activates protein kinases +* Activation of protein kinases +* Phosphorylation of tyrosine hydroxylase +* Increased catecholamine synthesis +* Increase in transmitter release +* Increase in post-synaptic response + +
+ +Note: + + + +--- + +## Summary + +* Signaling exists in all neurons to help them adjust to their environment +* Lots of ways to do this. There are various: +* Signals +* Receptors +* G-proteins +* 2nd messengers +* Downstream targets + +Note: + + +---